Gray level addressing for LCDs

- In Focus Systems, Inc.

Method and apparatus for providing gray level addressing for passive liquid crystal display (LCD) panels having overlapping row and column electrodes defining pixels are disclosed. Depending upon whether the rows are being addressed by "standard" or "Swift" addressing, the signals for applying to the column electrodes are determined by different calculations, in all of which modes the amplitudes of the column signals are related to the gray level desired to be displayed by the individual pixels. For a split interval system, column signals of appropriate amplitude and polarity are applied during different subintervals of a characteristic time interval of the display panel depending upon the method of addressing the rows. In the full interval mode, the column signals applied over a full time interval are based on the desired gray level of all the pixels in the column, adjusted to provide the proper rms voltage across all the pixels so that they display the desired gray levels.

Skip to:  ·  Claims  ·  References Cited  · Patent History  ·  Patent History

Claims

1. A method for addressing a passive flat panel display in which a plurality of overlapping first and second electrodes on opposite sides of an electro-optical material define a matrix of pixels that display in a frame period information in more than two gray levels, the display being characterized in that the optical state of each pixel is determined by the rms voltage appearing across the pixel over the frame period, the method comprising:

applying first signals that are independent of the information to be displayed to the first electrodes during characteristic time intervals of each frame period;
applying second signals of changing pulse height magnitudes and representative of the information to be displayed to the second electrodes during each frame period, the magnitude of each second signal at any time being chosen from more than two available voltages and being related to the desired gray level of at least one pixel defined by the corresponding second electrode and selected one or ones of the first electrodes.

2. The method of claim 1, in which the desired gray levels of pixels are represented by pixel information elements, the values of which vary between a lower limit and an upper limit, and further comprising

generating at least one virtual first signal for at least one virtual first electrode overlapping said second electrodes providing a plurality of virtual information elements; wherein
said first signals are applied to select said first electrodes and said virtual first electrodes sequentially; and
the amplitude of each second signal is proportional to the pixel information element and the virtual information element of the selected first electrode, respectively, during said time interval.

3. The method of claim 1 in which:

said first signals select each first electrode during more than one time interval over each said frame period;
the desired gray levels of pixels are represented by pixel information elements, the values of which vary between a lower limit and an upper limit; the method further comprising
generating at least one virtual first signal for at least one virtual first electrode overlapping said second electrodes providing a plurality of virtual pixels having virtual information elements; wherein
the amplitude of each second signal at any time interval is proportional to the sum of the products of the amplitude of each first signal at that time interval and the pixel information element at that first electrode; and
adjusted by a term that is proportional to the sum of the products of the amplitude of said virtual first signal at said time interval and the virtual information element at that virtual first electrode.

4. The method of claim 3 in which a single virtual pixel is associated with each second electrode.

5. The method of claim 3 which multiple virtual pixels are associated with each second electrode.

6. The method of claim 1 in which each first signal selects a corresponding first electrode during multiple characteristic time intervals within the frame period.

7. The method of claim 6 in which the selections are distributed throughout the frame period.

8. The method of claim 1 in which each first signal applies to the corresponding first electrode a zero voltage during characteristic time intervals in which the corresponding first electrode is not selected.

9. The method of claim 1 in which at least some of the first signals cause no more than one selection of their corresponding first electrodes during a frame period.

10. The method of claim 1 in which the magnitude of a second signal during a characteristic time interval is determined by the sum of first and second quantities, the first quantity being proportional to a sum of products of the value of the information element of each pixel defined by the overlapping of the corresponding second electrode and first electrodes selected during the time interval by corresponding first signals and the amplitude of the corresponding first signal and the second quantity including a term related to the square of the values of at least some of the information elements of the pixels defined by the corresponding second electrode.

11. The method of claim 10 in which the first quantity is equal to zero during at least one but not all of the characteristic time intervals of the frame period.

12. The method of claim 10 in which during at least one characteristic time interval of the frame period, a second signal is generated and applied when none of the first electrodes is selected.

13. The method of claim 10 in which the second quantity is equal to zero during at least one but not all of the characteristic time intervals of the frame period.

14. The method of claim 10 in which the first quantity is non-zero in at least one characteristic time interval, the second quantity is non-zero in at least one characteristic time interval, and in no characteristic time interval are both the first and second quantities non-zero.

15. The method of claim 1 in which

applying second signals includes applying a second signal having during at least some characteristic time intervals of the frame period an amplitude determined by the amplitudes of the first signals causing selections during the characteristic time interval and by pixel input data corresponding to more than two gray levels of pixels defined by the corresponding second electrode; and
generating an additional signal and applying it to at least some of the second electrodes at a time during the frame period when none of the first electrodes is selected, the additional signal producing across corresponding pixels an rms voltage over the frame period related to the pixel input data.

16. The method of claim 15 in which the magnitude of the additional signal is determined by the sum of the squares of pixel input data of multiple pixels defined by the corresponding second electrode.

17. The method of claim 1, in which the desired gray levels of the pixels are represented by pixel information elements, the values of which vary between a lower limit and an upper limit, and in which the magnitude of at least one of the second signals during a characteristic time interval is determined by the value of the information element of each pixel defined by the intersection of the corresponding second electrode and selected ones of the first electrodes and by a term related to the sum of the squares of the values of at least some of the information elements of the pixels defined by the corresponding second electrode.

18. The method of claim 1, in which the desired gray levels of the pixels are represented by pixel information elements, the values of which vary between a lower limit and an upper limit, and in which the magnitude of at least one of the second signals during a characteristic time interval is related to the square root of a quadratic equation including as a variable the value of the pixel information element of at least one first electrode selected by a corresponding first signal.

19. The method of claim 1, in which the desired gray levels of the pixels are represented by pixel information elements, the values of which vary between a lower limit and an upper limit, and in which multiple virtual information elements are defined by virtual pixels defined by a virtual first electrode overlapping the second electrodes, the method further including applying to the second electrodes second signals having magnitudes related to the values of the information elements and the virtual information elements of the respective pixels and virtual pixels defined by the corresponding second electrode and selected ones of the respective first or virtual first electrode.

20. The method of claim 19 in which each of the first electrodes and virtual first electrodes is periodically selected and the magnitudes of the second signals are proportional to the information elements of the pixels defined by the overlap of the corresponding second electrodes with the selected one of the first electrodes and the virtual first electrodes.

21. The method of claim 19 in which each of the first electrodes and virtual first electrodes is selected multiple times during the frame period and the magnitudes of the second signals are proportional to the information elements of the pixels or virtual pixels defined by the overlap of the corresponding second electrodes with the selected one or ones of the first electrodes and the virtual first electrodes.

22. The method of claim 19 in which the magnitudes of the second signals are proportional to the virtual information elements of the virtual pixels defined by the overlap of the corresponding second electrodes with the virtual first electrode during time intervals in which no first electrode is selected.

23. The method of claim 19 further comprising:

generating at least one virtual first signal for at least one virtual first electrode that defines a plurality of virtual pixels each corresponding to a second electrode and represented by a virtual information element having a value determined from the values of more than one pixel information element representing pixels defined by the corresponding second electrode; and in which
the magnitude of at least one of the second signals at any time interval is determined by a sum of first and second quantities, the first quantity being proportional to the sum of the products of the amplitude of each first signal causing a selection of a first electrode at that time interval and the pixel information element of the pixel defined by the corresponding first and second overlapping electrodes and the second quantity representing a sum of quantities derived for each of the virtual rows, each virtual row contributing to the sum a quantity proportional to the product of the amplitude of the corresponding virtual first signal at the time interval and the virtual information element of the virtual pixel defined by the virtual first electrode and the corresponding second electrode.

24. The method of claim 19 further comprising:

generating at least one virtual first signal for at least one virtual first electrode that defines a plurality of virtual pixels, each corresponding to a second electrode and represented by a virtual information element having a value determined from the values of more than one pixel information element representing pixels defined by the corresponding second electrode; and in which
the magnitude of at least one second signal is related during at least one characteristic time interval of the frame period to a sum of the products of the amplitude of each first signal causing a selection of a first electrode at that time interval and the pixel information element of the pixel defined by the corresponding first and second overlapping electrodes and the magnitude of at least one of the second signals being related during at least one characteristic time interval of the frame period to a product of the amplitude of a virtual first signal during the time interval and the virtual information element of the virtual pixel defined by the corresponding virtual electrode and the corresponding second electrode.

25. The method of claim 24 in which the magnitude of at least one second signal during at least one time interval of the frame period is related to a sum of products of the amplitude of corresponding virtual first signals at the time interval and virtual information elements of virtual pixels defined by the virtual electrode and the corresponding second electrode.

26. The method of claim 24 in which the magnitude of at least one second signal is related during different characteristic time intervals of the frame period to a sum of the products of the amplitude of each first signal causing a selection of a first electrode at that time interval and the pixel information element of the pixel defined by the corresponding first and second overlapping electrodes or to a product of the amplitude of a corresponding virtual first signal at the time interval and the virtual information element of the virtual pixel defined by the virtual electrode and the corresponding second electrode.

27. The method of claim 24 in which the magnitude of at least one second signal is related during a single characteristic time intervals of the frame period to a sum of the products of the amplitude of each first signal causing a selection of a first electrode at that time interval and the pixel information element of the pixel defined by the corresponding first and second overlapping electrodes or to a product of the amplitude of a corresponding virtual first signal at the time interval and the virtual information element of the virtual pixel defined by the virtual electrode and the corresponding second electrode.

28. The method of claim 1, in which the desired gray levels of the pixels are represented by pixel information elements, the values of which vary between a lower and an upper limit, and in which the magnitude of each second signal during the time interval is proportional to a sum of products of the value of the information element of each pixel defined by the corresponding second electrode and the amplitude of the first signal of the corresponding first electrode, the magnitude of the second signal being determined by adding to the product a term related to the square of the values of the information elements of the pixels defined by the corresponding second electrode.

29. A method for addressing a passive flat panel display in which a plurality of overlapping first and second electrodes on opposite sides of an electro-optical material define a matrix of pixels that display in a frame period information in more than two gray levels, the display being characterized in that the optical state of each pixel is determined by the rms voltage appearing across the pixel over the frame period, the method comprising:

generating a series of first signals that are independent of the information to be displayed;
applying the first signals to the first electrodes during characteristic time intervals of each frame period;
generating a series of second signals of changing pulse height magnitudes and representative of the information to be displayed;
applying the second signals to the second electrodes during the characteristic time intervals of each frame period;
the magnitudes of the second signals at any time during a characteristic time interval being chosen from more than two available voltages and being related to the desired gray level of at least one pixel defined by the corresponding second electrode.

30. Apparatus for addressing a passive flat panel display in which a plurality of overlapping first and second electrodes on opposite sides of an electro-optical material define a matrix of pixels that display information in a more than two gray levels, the display being characterized in that the optical state of each pixel is determined by the rms voltage appearing across the pixel over the frame period, the apparatus comprising:

means for driving the first electrodes during characteristic time intervals of each frame period with first signals which are independent of the information to be displayed; and
means for driving the second electrodes during each frame period with second signals, each of which is representative of the information to be displayed and whose pulse height amplitude at any time is chosen from more than two available voltages and is related to the desired gray level of at least one of the pixels defined by the second electrode.

31. Apparatus for converting video signals including control components and information components into signals for addressing a passive flat panel display in which a plurality of overlapping first and second electrodes on opposite sides of electro-optical material define a matrix of pixels that display information in more than two gray levels, the display being characterized in that the optical state of each pixel is determined by the rms voltage appearing across the pixel over the frame period, the apparatus comprising:

first signal generating means for generating a series of first signals which are independent of the information component of the video signals;
means for applying the first signals to the first electrodes during characteristic time intervals of each frame period;
second signal generating means for generating during subintervals of the characteristic time intervals second signals of changing pulse height magnitude selected from more than two available voltages and representative of the information component of the video signals including gray levels and the amplitude of each of which at any time is related to the desired gray level of at least one of the pixels;
means for applying the second signals to the second electrodes during each frame period coincidentally with the application of the first signals to the first electrodes.

32. The apparatus of claim 31, including:

control signal generating means for generating control signals related to the control components of the video signals; and
the means for applying the first and second signals to their respective electrodes being controlled by the control signal generating means.

33. The apparatus of claim 31, in which:

the desired gray levels of the pixels are represented by pixel information elements, the values of which vary between a lower limit and an upper limit;
said first signal generating means including means for generating at least one virtual first signal for at least one virtual first electrode overlapping said columns providing a plurality of virtual information elements;
said means for applying said first signals applies said first signals to select said first electrodes and said virtual first electrodes sequentially; and
said second signal generating means generates second signals the amplitude of each of which is proportional to the pixel information element and the virtual information element of the selected first electrode, respectively, during the time interval that each said first electrode is selected.

34. The apparatus of claim 31, in which:

said first signal generating means generates first signals that select each first electrode more than once during a frame period;
the desired gray levels of the pixels are represented by pixel information elements, the values of which vary between a lower limit and an upper limit;
said second signal generating means includes means for generating at least one virtual first signal for at least one virtual first electrode overlapping said second electrode providing a plurality of virtual information elements; and
said second signal generating means generates second signals the amplitude of each of which at any characteristic time interval is proportional to the sum of the products of the amplitude of each first signal at that time interval and the pixel information element at that first electrode, adjusted by a term that is proportional to the sum of the products of the amplitude of said virtual first signal at said time interval and the virtual information element at that virtual first electrode.

35. The apparatus of claim 31, in which:

the first signal generating means generates first signals that are orthonormal functions selecting each first electrode more than once during a frame period;
the desired gray levels of the pixels are represented by pixel information elements; and
the second signal generating means includes dot product generating means for generating a dot product term of each first signal and the corresponding bit plane of the pixel information element.

36. The apparatus of claim 35, in which:

said first signal generating means includes means for generating at least one virtual first signal for applying to a virtual first electrode;
said second signal generating means includes means for generating a plurality of virtual information elements for at least one virtual first electrode overlapping said second electrodes;
adjustment term generating means for generating an adjustment term that is proportional to the sum of the products of the amplitude of said virtual first signal and the virtual information element at the corresponding virtual first electrode, and combiner means for combining said dot product term and said adjustment term to provide said second signal.

37. The apparatus of claim 34 in which each first signal selects a corresponding first electrode during multiple characteristic time intervals distributed within the frame period.

Referenced Cited
U.S. Patent Documents
3955187 May 4, 1976 Bigelow
3997719 December 14, 1976 Judice
4043640 August 23, 1977 Berreman
4427978 January 24, 1984 Williams
4508427 April 2, 1985 Ross
4560982 December 24, 1985 Sonehara et al.
4709995 December 1, 1987 Kuribayashi et al.
4743096 May 10, 1988 Wakai et al.
4752774 June 21, 1988 Clerc et al.
4766430 August 23, 1988 Gillette et al.
4769713 September 6, 1988 Yasui
4776676 October 11, 1988 Inoue et al.
4808991 February 28, 1989 Tachiuchi et al.
4818078 April 4, 1989 Mouri et al.
4840460 June 20, 1989 Bernot et al.
4840462 June 20, 1989 Hartmann
4929058 May 29, 1990 Numao
4991022 February 5, 1991 Canfield et al.
5010327 April 23, 1991 Wakita et al.
5055833 October 8, 1991 Hehlen
5062001 October 29, 1991 Farwell et al.
5091722 February 25, 1992 Kitajima et al.
5134495 July 28, 1992 Frazier
5157387 October 20, 1992 Momose et al.
5189406 February 23, 1993 Humphries et al.
5280280 January 18, 1994 Hotto
5420604 May 30, 1995 Scheffer et al.
5489918 February 6, 1996 Mosier
5489919 February 6, 1996 Kuwata et al.
5583530 December 10, 1996 Mano et al.
Foreign Patent Documents
0127701 December 1984 EPX
0569974 November 1993 EPX
Other references
  • Yoshio Suzuki, Mitsunobu Sekiya, Kunihiko Arai and Akio Ohkoshi, "A Liquid-Crystal Image Display," SID 83 Digest, 32-33. Sprokel, Gerald J., "The Physics and Chemistry of Liquid Crystal Devices," pp. 105-113, 1980. Hideaki Kawakami, Hisao Hanmura and Eiji Kaneko, "Brightness Uniformity in Liquid Crystal Displays," SID Digest, 28-29. Ruckmongathan, "A generalized addressing technique for RMS responding Matrix LCDs," 1988 IDRC, pp. 80-85. Lagerwall, "Ferroelectric Liquid Crystal for Displays," 1985 IDRC, pp. 213-221. "1988 International Display Research Conference" T.M. Ruckmongathan pp. 80-85. "Pulse-Height Modulation (PHM) Gray Shading Methods for Passive Matrix LCD's" T. J. Scheffer. Japan Display 92, pp. 69-71.
Patent History
Patent number: 5767836
Type: Grant
Filed: Jun 7, 1995
Date of Patent: Jun 16, 1998
Assignee: In Focus Systems, Inc. (Wilsonville, OR)
Inventors: Terry J. Scheffer (Portland, OR), Arlie R. Conner (Portland, OR), Benjamin R. Clifton (Oregon City, OR)
Primary Examiner: Amare Mengistu
Law Firm: Stoel Rives LLP
Application Number: 8/486,369
Classifications
Current U.S. Class: 345/147; Gray Scale Capability (e.g., Halftone) (345/89)
International Classification: G09G 336;